U.S. Pat. No. 3,773,000 issued Nov. 20, 1973 discloses an air curtain apparatus in which a wheel mounted air supply tube is hingedly connected to a nozzle structure disposed in transverse relation to the air supply tube at the outlet end of the air supply tube. The hinged connection is designed to allow the nozzle portion of the apparatus to swing alongside of the air inlet tube in order to facilitate the transport of the apparatus from one job to another. One objection to this type of apparatus is that it is of considerable width due to the side by side orientation of the air supply tube and the nozzle. Also, the hinged connection is cumbersome and time consuming to manipulate properly.
Another known apparatus for supplying an air curtain to a pit for burning material within the pit is disposed alongside the pit and includes an elongated nozzle tube having air outlets along the length and which is supplied with air from one end thereof through a coaxial air supply tube. With such apparatus it is difficult to insure a uniform volume of air throughout the entire length of the pit due to changes in the velocity of air flow along the length of the conduit due to friction between the air and the inner surfaces of the nozzle structure.
Still another known arrangement for supplying a curtain of air to a pit containing material to be burned includes an air inlet tube connected at its air outlet end with a transversely disposed nozzle structure, the interconnection between these two elements being in the form of complementary flanges which are bolted together. Obviously such an arrangement is difficult to manipulate since the bolt holes in the cooperating flanges must be aligned and because uneven conditions of the ground near the pit further enhance the difficulty of making the bolted connection between the cooperating flanges.